The U.S. Marine Corps has bought 4,200 new light machine-guns. The new weapon, the M27, will replace the current M249s in marine infantry battalions. However, each of these battalions will retain six M249s, to give the battalion some options. The marines will withdraw from service 20 percent of their 10,000 M249s by the time all 4,200 M27s have been delivered.
The M27 is a 3.6 kg (7.9 pound, empty) automatic weapon based on the HK416. It has a forward grip and heavier barrel and can use a 30 or 100 round magazine. Unlike the M249, it does not have an easily replaceable barrel, but it is more accurate and has a slower rate of fire (560-640 rounds per minute). The M27 uses a mechanical system that is less likely to jam, as well as a floating barrel (for better accuracy.) Marines are expected to use fewer rounds of more accurate fire with the M27 than they did with the M249.
The M27 came after five years of research and development to create a weapon that would replace the M249, which the army and marines began using in the early 1980s. The marines have had a lot of complaints about the M249 in Iraq (jams from all the dust and sand), and many of the marine M249s are simply wearing out.
The marines were originally looking for an IAR (Infantry Automatic Rifle) that weighed between 4.8 kg (10.5 pounds) and 5.7 kg (12.5 pounds) empty, used a large magazine (100 rounds or more) as well as the standard M-16 30 round magazine. The heavy barrel on the IAR had to be able to handle sustained fire of 36-75 rounds a minute. The higher number was the ideal. It had to have the standard rail on top for mounting accessories, be resistant to jamming from dust and sand and, in general, be a lot better than the M249. The marines always planned to buy 4,000 weapons initially, and wanted to do so as soon as possible.
The M249 weighs 6.8 kg (15 pounds) empty, and has been popular with the troops. But in over two decades, despite several tweaks to the basic design, many complaints have piled up. The marines were not the first ones to take action on a replacement. Six years ago SOCOM (U.S. Special Operations Command) began using the Mk 46 LMG (Light Machine Guns). This weapon is a modified version of the American M249 squad automatic weapon (SAW), which is in turn a modified version of a European design from the Belgian firm FN. The Mk 46 is lighter, at 5.9 kg (13 pounds) empty, 8.2 kg (18 pounds) loaded, with 200 rounds, compared to 10 kg (22 pounds) for the M249. The Mk 46 also has the rail on top for the quick attachment of sights and such. The lighter weight was accomplished with a newly designed barrel, and removing various bits of hardware SOCOM didn't want. Added is a forward pistol grip and a detachable bipod. SOCOM likes to use the Mk 46 more like a "heavy assault rifle" than a "light machine-gun."
U.S. Army Special Forces pioneered the development of the 5.56mm light machine-gun four decades ago, when they obtained the first experimental models for use in Vietnam. The Special Forces and SEALs were very impressed with the light weight, and heavy firepower, from these weapons. But it took over a decade for the regular army to adopt such a weapon, mainly in response to the success the Russians were having with their own version of the lightweight squad machine-gun.
The army is also making noise about an M249 replacement, and have followed the marine search with great interest. The marines finally selected the lighter HK entry after three months of field testing. The M27 is quite similar to the first American "light machine gun", the M1918 BAR (Browning Automatic Rifle). This was a 7.62mm, 7.25 kg (16 pound) automatic rifle, similar in appearance to the later (1950s), and lighter M-14. The BAR was revolutionary in World War I, and was used by the United States until the 1960s, when it was replaced with 6.6 kg M-14A1s equipped with a heavier barrel. This was not a satisfactory solution, and led to the development of the M249.